A weekly magazine SPA reported some towns rankings. According to the magazine, the following 5 towns are dangerous, because they have a lot of naughty ones.
Hiratsuka, in Kanagawa prefecture
The magazine reporter says; Hiratsuka has totally stupid taste. There are many affrays in summer.
Kawasaki, in Kanagawa prefecture
The magazine reporter says; You can see motorcycle gang girls in parks. Kawasaki has strong naughty ones taste.
Akabane, in Tokyo
The magazine reporter says; Akabane is the hometown of one of the Chinese gangs.
Sagamihara, in Kanagawa
The magazine reporter says; Motorcycle gangs run actively in Sagamihara.
Ageo, Saitama prefecture
The magazine reporter says; Gang members are sitting around the station. It is scary.
Figure: Map of worst 5 towns
Source is SPA magazine, 2015 March 10 edition.